1. Field of the Invention
The present invention relates to a method of processing an amorphous material such as an inorganic glass material.
2. Prior Art
As an amorphous material, glass has a high hardness and homogenous physical properties, and is also cheap, and hence is used in a variety of fields.
For example, if a glass substrate having minute projections formed on a surface thereof is used in a liquid crystal display element, then the projections fulfill a role of determining the length of the so-called cell gap in the liquid crystal display element. Without using glass beads for adjusting the cell gap, therefore, a liquid crystal display element having a desired cell gap can be manufactured.
Moreover, if a glass substrate having such minute projections or minute undulations formed on a surface thereof is used in an optical disk or a magnetic-optical disk, then the minute projections or minute undulations fulfill an important role in signal reading. Moreover, such a glass substrate is an important component in the manufacture of an optical diffraction grating having regularly arranged projections.
Furthermore, such glass substrates are also widely used as magnetic disk substrates in hard disk drives (HDDs).
In an HDD, a driving method called the CSS (contact start stop) method is commonly adopted. In this method, a magnetic head of the HDD contacts the disk surface when the disk is stationary, and then when the HDD is started up, the magnetic head is made to rise up slightly from the disk surface and the disk is rotated at high speed.
When an HDD is driven using the CSS method, it is common to form minute undulations referred to as texture on a surface of the glass substrate, to prevent the magnetic head from sticking to the disk when the magnetic head is made to rise up during startup and reduce friction during startup and stopping. Although glass is a brittle material and hence shape processing is much more difficult to carry out than with a plastic material, because glass is useful as a disk substrate, various methods of forming such minute undulations on a surface of a glass substrate have been developed and put to practical application in the past.
For example, Japanese Laid-open Patent Publication (Kokai) No. 64-42025 discloses art in which minute undulations are formed on a glass substrate by etching using a fluorine-containing liquid or hydrogen fluoride gas (prior art 1).
Moreover, Japanese Laid-open Patent Publication (Kokai) No. 7-296380 discloses art in which a glass substrate is subjected to crystallization treatment and a surface of the glass substrate is mirror polished, and then treatment is carried out using an etching solution prepared by adding sulfuric acid or ammonium fluoride to hydrofluoric acid, thus forming minute undulations on the surface of the glass substrate (prior art 2).
Furthermore, Japanese Laid-open Patent Publication (Kokai) No. 8-249654 discloses art in which ultrafine particles are applied in a mono-dispersed state onto a surface of a substrate, a surface protecting layer is next etched by dry etching, and then the ultrafine particles are removed, thus forming minute undulations on the surface of the substrate (prior art 3).
Moreover, Japanese Laid-open Patent Publications (Kokai) Nos. 7-182655 and 9-194229 disclose art in which a laser beam of a predetermined energy is irradiated onto a surface of a glass substrate to cause the surface to rise up at the places of laser beam irradiation, thus forming projections on the surface of the glass substrate (prior art 4).
However, in the case of the above-mentioned prior art 1, etching is merely carried out on a glass having a predetermined chemical composition using a fluorine-containing liquid or hydrogen fluoride gas. There is thus a problem that a rough surface is formed with the surface undulations having an uneven projection height; it is difficult to obtain a texture having a uniform projection height.
Moreover, in the case of the above-mentioned prior art 2, a glass substrate is subjected to crystallization treatment to form a crystallized layer and an amorphous layer, and surface undulations are formed on the glass substrate by utilizing the difference in etching rate between the crystallized layer and the amorphous layer. There is thus a problem that the method cannot be applied to a normal homogenous glass material.
Furthermore, in the case of the above-mentioned prior art 3, ultrafine particles are coated onto a substrate, dry etching is next carried out, and then the ultrafine particles are removed. As is different to normal etching treatment in which masking is carried out using a metallic mask, it would appear that minute surface undulations can be formed, but there is a problem that dry etching is slow, resulting in high costs and in the method not being suited to mass production.
Moreover, in the case of the above-mentioned prior art 4, a laser is irradiated onto a surface of a glass substrate, and hence there is a problem that the method can only be applied to a glass material that has a large absorption coefficient at a particular wavelength of the laser light. Moreover, the height of the projections formed is very sensitive to the output power of the laser, and hence there is a problem that it is difficult to obtain uniform projections of a desired height.
All of the prior art described above thus suffers from the problem that it is still not possible to form minute undulations having a uniform projection height, or to carry out mass production. Furthermore, in recent years there have been calls in the HDD field for disks of ever higher density. As the density of disks is increased, it becomes necessary to make the projection height of the surface undulations of glass substrates as low as possible and as uniform as possible.